Avoid anything that gets the testicles over heated, as excess heat can damage sperm-this is why the testicles are external and not inside the body. Things that may cause overheating are:laptops on the lap, saunas, hot baths, tight underwear, cycling, medical conditions such as varicoele (varicose veins in scrotum-if you think you have this see your doctor)

Stop smoking as smokers have higher incidence of sperm problems

Keep alcohol consumption within safe limits

Eat a balanced healthy diet high in antioxidants, eat lots of fruit and veg & cut down on the meat-make sure he gets his 5 a day. A recent Spanish study has shown that men who eat a lot of fruit and vegetables, in particular peppers, spinach and citrus fruits, have higher quality and faster swimming sperm.

Check if he is on any medication that may damage sperm e.g. some antidepressants, check with your doctor.

Exercise moderately-remember keep those testicles cool, and wear loose fitting boxers and clothes. May be best to avoid the tight lycra